Q&A # 162 - February 14, 2000
Q I saw an amplifier spec sheet that said Signal-to-Noise Ratio, A-Weighted. What does that mean?
A A-Weighted means that a filter has been applied to the data. The A-Weighting curve is seen in the graph shown below (copyright Audio Precision). Assigning a dB value of 0 at 1 kHz, the graph shows the relative response of the human ear to frequencies between 20 Hz and 30 kHz. So, for example, at 2 kHz, the ear is a couple dB more sensitive than it is at 1 kHz. At 20 kHz, the ear is about 8 dB less sensitive, and at 20 Hz, it is about 50 dB less sensitive. So, with the A-Weighting, all noise above the curve is eliminated from the calculations, implying that the human ear can't hear it anyway. Simply put, it is a way of making the specs look better, but it is useful in scientific terms.
Q I purchased Jamo P-220 floor standing speakers about a month ago. I'm pretty happy with their performance, but I noticed that some notes seemed to bloat . . . if that is the correct word to use. At first I thought it might have been the placement of the speakers, so I tried a variety of placement techniques to no avail, and I was beginning to suspect that the rear port could be the culprit. I was lucky enough to stumble on a review on the P-210 which is a slightly smaller version of the P-220 but with the same drivers and ports. The review was very positive but found that there seemed to be a lot of midrange port leakage just over 1 kHz. Unfortunately, I don't have the page on how he worked around this problem. I find that if I use a parametric equalizer to reduce the frequencies around the 800 Hz - 1 kHz range on the P-220, that the problem is reduced, but the sound remains muddy, probably due to the midrange contribution of the port. Is there any material I could stuff in the port that will absorb frequencies in the 1 kHz area?
A Equalizers help for certain problems, but they are not a panacea. I would suggest using a little EQ along with some polyester pillow stuffing that you can purchase at any bedding supply store. You can also get this kind of material at speaker supply stores. The 800 Hz area is notorious, and it makes the sound nasal. Overuse of EQ just makes it sound like someone threw a blanket over the speaker. It might be that the crossover network in the speaker needs some redesign.
Q I live in an apartment and have a home theater setup. My equipment comprises the following: Paradigm Titans for the mains, Paradigm CC-150 for the center, Paradigm Atoms for the rear, Sound Dynamics 8" powered subwoofer, Sony STR-DE525 receiver, Proscan PS8610P DVD player, and a Technics 110+ mega CD changer. My system sounds great when watching movies in DD or DPL, but when listening to music, it has too much bass. The subwoofer level is only at 2, and the LP filter is set to 100 Hz. Can you give me advice on the best place to put the subwoofer and what level it should be set to?
A First, just lower the LP crossover setting to about 50 Hz, or maybe even lower. I think you are probably getting too much in the 80 Hz region, which makes the sound "boomy". You might also move the subwoofer a little farther out from the wall, and don't put it in the corner. However, use the lower LP setting first. That may completely cure your problem.
Q I have approximately 20 hours of 20 - 25 year-old, home-recorded, cassette music tapes. I wish to digitize the tapes and turn the results into a CD for our family's enjoyment. These tapes consist primarily of a single instrument -- mandolin or harmonica -- being played into an inexpensive cassette tape recorder. How should I proceed?
A We will be publishing a technical article on using your PC's CD-R/W to do this, including converting them to MP3, pretty soon.
Q I have a home theater system consisting of a NAD T750 surround receiver, B&W 602 S2 front speakers, B&W CC6 center, and two B&W DM302s as surround speakers. I've been looking for a subwoofer in the area of $500 - $700 range. I've been considering the B&W ASW500 or 1000. I was wondering if you could give me advice as to which subwoofer you think would suit my system?
A I would suggest going an extra $100 and getting the Velodyne CT-150 (MSRP $799). I have not heard anything better at that price.
Q If I was considering doubling up on my center channel, what is the most advisable way of approaching the setup? a) If the preamp/processor only has one center out, can I use a splitter or "Y" connection through another amp to send the signal to both center channels, or would this degrade the sound information? b) Is it better to place a center speaker above and below, or on either side of the TV? c) Will I be creating some sort of weird cancellation effect by doubling up my center channels?
A You can use a Y splitter to send the pre-out info to two power amplifiers and each amplifier can then drive its own center channel speaker. To try things out first though, I would suggest driving the two speakers with the same amplifier, wiring them in parallel if your amplifier is capable of handling low impedance loads, or in series if it cannot. Then, arrange your two center channel speakers with one above and one below the TV, followed by putting them at the sides. It may be that your single amplifier can handle the two speakers. Otherwise, if you decide you really like having the two center channel speakers, get a second amplifier to drive the second speaker.
Q I recently purchased a Toshiba 3109 DVD player with a built-in DD decoder and was hoping to use it. The problem is that my receiver (Yamaha RX-V990) only has 5 input channels without a sub input. The receiver is DD ready, so I should be able to get DD 5.1 by using the DD decoder on the DVD player, but where am I suppose to plug the sub output cable?
A Run the LFE output from the DVD player directly to the subwoofer with a coaxial RCA cable. Then, adjust the volume using the volume control on the back of the subwoofer. However, for the most part, the LFE channel just duplicates low frequencies in the other channels, so you can use the subwoofer output jack on your receiver to drive the subwoofer and get pretty much what is in the LFE channel anyway.
Q I'm just starting to build my home theater room. I have Paradigm Atom speakers for the fronts, a CC-170 center speaker, and Boston Acoustics for the rears. I have a Denon AVR-1800 receiver and a Velodyne CT-100 subwoofer. I am planning to buy a Panasonic 32" direct view TV. Does the video quality from a 480p SD direct view 32" television set such as Panasonic and a progressive scan DVD player have that much better resolution than a regular direct view TV set like the Panasonic CT-32sF36 and a regular DVD player that I'm considering purchasing? In other words, is it a big jump in video quality, or is it a video quality that can only be seen when the two formats are seen side by side together? Is it worth it to spend the extra money on the SD TV and progressive scan DVD player?
A If the the Panasonic SD model is a 16x9 monitor, and if it can accept a 480p, then yes it will look better. You probably have heard people talk about how good their video setup looks using a Faroudja line doubler. Well, a progressive DVD looks as good or better than the Faroudja line doubler! That is because the images are from real data. No computer-generated image can ever really take the place of real image data. Where the line doubler comes in handy is when you are dealing with 480i as the original signal. A normal TV only displays 240 lines at a time (interlaced, or the "i" in 480i). Field 1, which has lines 1, 3, 5, . . . 479. Then field 2, which has lines 2, 4, 6, . . . 480. This interlaced picture causes fine detail like brick walls and striped shirts to flicker. A progressive scan DVD player outputs all 480 lines at once, 1, 2, 3, 4, . . . 480. The flicker on brick walls and striped shirts are almost completely gone. I say almost because while DVD video may be stored in a progressive format on DVD, it has been filtered for interlaced playback and stored as field 1 and field 2. Also, playing the movie on a 16x9 monitor will give you 33% more resolution than a 4:3 monitor, unless it offers a squeeze mode. Progressive Scan is wonderful in any case. With the Toshiba SD-5109 (review coming), I have been able to see much more "depth" in the picture.
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